|Publication number||US7052999 B2|
|Application number||US 10/617,226|
|Publication date||May 30, 2006|
|Filing date||Jul 11, 2003|
|Priority date||Dec 26, 2002|
|Also published as||US20040127052|
|Publication number||10617226, 617226, US 7052999 B2, US 7052999B2, US-B2-7052999, US7052999 B2, US7052999B2|
|Inventors||Sung-Kwon Lee, Sang-Ik Kim, Jun-Hyeub Sun|
|Original Assignee||Hynix Semiconductor Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (6), Referenced by (3), Classifications (16), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to a semiconductor device; and, more particularly, to a method for fabricating a semiconductor device capable of reducing a parasitic capacitance of a semiconductor memory cell.
Hereinafter, there is provided descriptions on problems arose by using a conventional method for fabricating a semiconductor device with reference to an exemplified process for forming a storage node contact hole.
As shown, an inter-layer insulation layer 13 is deposited on a substrate 11 providing various elements such as a word line (not shown), an impurity contact region 12 and so forth, and then, the inter-layer insulation layer 13 is selectively etched to form contact holes exposing the impurity contact region 12. Herein, the inter-layer insulation layer 13 is called a word line insulation layer.
Next, a plurality of plugs 14 for a storage node contact or a bit line contact are formed. Each plug 14 is buried into each contact hole, and thereby being contacted to the exposed impurity contact region 12.
It is common to use polysilicon for the plug 14; however, it is recently a frequent case that a stack structure including a tungsten layer and a barrier metal layer such as Ti/TiN generally used as a diffusion barrier layer is used for the plug 14 instead of the polysilicon.
Subsequent to the plug 14 formation, a diffusion barrier layer 15 having the typical structure of Ti/TiN is formed on the entire substrate structure. The diffusion barrier layer 15 is for suppressing a source gas used for depositing a subsequent metal layer 16 for a bit line (hereinafter referred to as a bit line metal layer) from reacting with the plug 14 and the impurity contact region 12. Then, on top of the diffusion barrier layer 15, the bit line metal layer 16 is formed by using polysilicon, tungsten or metal alloys such as tungsten nitride, tungsten silicide and so forth.
Next, such material as undoped silicate glass (USG) is used to form a buffer layer 17. The buffer layer 17 is for reducing stress easily generated between the bit line metal layer 16 and a nitride layer 18 commonly used as a hard mask. Herein, a process for forming the buffer layer 17 is omitted.
The nitride layer 18 for a hard mask (hereinafter referred to as a hard mask nitride layer) is typically made of nitride-based materials such as polysilicon nitride or silicon nitride.
The higher level of integration in a semiconductor device makes it difficult to stably secure overlay accuracy and a process margin of a pattern formation with use of a photoresist. Therefore, a self-aligned contact (SAC) process is employed since it uses pre-deposited existing materials without using an additional hard mask during the formation of the pattern, e.g., a contact hole. As a result, the SAC process is capable of reducing the fabrication costs. Among various etching methods of the SAC process, a nitride layer is typically used as an etch stop layer. Therefore, the SAC process etches an insulation layer under a condition that the nitride layer encompasses sidewalls and an upper part of a conductive pattern such as a gate electrode or a bit line and an oxide layer is subsequently etched in a higher rate than the nitride layer.
The SAC process is also employed for a storage node contact formation. Thus, a nitride-based etch stop layer 19 is deposited along the upper part and sidewalls of the bit line in order to prevent a bit line loss during the SAC process.
As shown in
Next, the bit line insulation layer 21 is planarized by performing a chemical mechanical polishing (CMP) process with a target that the bit line insulation layer 21 remains with a predetermined thickness on top of the hard mask nitride layer 18. A photoresist pattern 22 for forming a storage contact is formed thereafter. The bit line insulation layer 21 and the etch stop layer 19 are sequentially etched with use of the photoresist pattern 22 as an etch mask. This etch process is the SAC etch process. From this SAC etch process, a contact hole 23 exposing a surface of the plug 14 allocated between the bit lines is formed.
Prior to forming the contact hole 23, a typical process for forming a contact pad is additionally performed to improve an overlap margin of a process for forming the contact. However, in this section, detailed descriptions on this process are omitted.
After the SAC process, the nitride-based etch stop layer 19 is etched so that a spacer 20 is formed at a sidewall of each bit line.
Meanwhile, a silicon nitride layer, which is the most common nitride layer, has a dielectric constant of about 7.5. This value is higher than that of a silicon oxide layer, which is the most common oxide layer. As a reference, the dielectric constant of the silicon oxide layer is about 3.9.
When this plug structure formed by the SAC process is applied to a capacitor contact hole formation in a dynamic random access memory device, that is, the capacitor contact hole is formed by etching a space between the bit lines through the SAC process, a bit line capacitance is increased compared to the typical contact structure that a bit line and a capacitor contact plug, which is fundamentally a charge storage electrode, are insulated with an oxide layer such as silicon oxide. This increased bit line capacitance means an increase of a parasitic capacitance, which, in turn, decreases a cell capacitance.
Accordingly, it is necessary to develop a process for securing a stable SAC etch profile as simultaneously as for minimizing the decrease of the cell capacitance.
It is, therefore, an object of the present invention to provide a method for fabricating a semiconductor device capable of decreasing a parasitic capacitance to thereby increase a cell capacitance.
In accordance with an aspect of the present invention, there is provided a method for fabricating a semiconductor device, including the steps of: (a) forming a plurality of conductive patterns arranged with a predetermined spacing distance on a substrate, each conductive pattern including a conductive layer and a hard mask nitride layer; (b) forming a planarized inter-layer insulation layer on an entire surface of the resulting structure from the step (a); (c) etching the inter-layer insulation layer through the use of a wet etching process or a dry etching process so that a height of the inter-layer insulation layer is lower than that of the hard mask nitride layer; (d) forming an etch stop layer along the inter-layer insulation layer; (e) forming a self-aligned contact hole of which partial portion expands towards each conductive pattern by etching selectively the etch stop layer and the inter-layer insulation layer until a surface of a partial portion of the substrate disposed within the predetermined spacing distance is exposed and; and (f) forming a self-aligned contact structure by filling the self-aligned contact hole with a conductive material.
The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:
Hereinafter, with reference to
Next, a plug 33 for making a contact to a storage node or a bit line is formed by filling the contact hole. Concurrently, the plug 33 is also contacted to the exposed impurity contact region 31. Herein, the plug 33 includes the typical landing plug contact (LPC) contacted to the impurity contact region 31 of the substrate 30.
The plug 33 is generally made of polysilicon. Recently, a structure including multiple layers of a tungsten layer and a barrier metal layer using Ti/TiN is frequently used instead of the polysilicon.
Subsequent to the plug 33 formation, a process for forming a contact pad on the plug 33 is then performed; however, detailed descriptions on this process is omitted for the sake of convenience. Herein, a second inter-layer insulation layer 34 is deposited on the entire resulting structure including the plug 33.
A diffusion barrier layer 35 having the typical structure of Ti/TiN is formed on the second inter-layer insulation layer 34. The diffusion barrier layer 35 is for suppressing a source gas used for forming a metal layer 36 for a bit line (hereinafter referred to as a bit line metal layer) from reacting with the plug 33 and the impurity contact region 31. Then, the bit line metal layer 36 is formed with such metal as tungsten, polysilicon and so forth or metal alloys such as tungsten nitride, tungsten silicide and so forth.
After the bit line metal layer 36 formation, a nitride layer 37 for a hard mask (hereinafter referred to as a hard mask nitride layer) is deposited through a plasma enhanced chemical vapor deposition (PECVD) technique or a low pressure chemical vapor deposition (LPCVD) technique. The hard mask nitride layer 37 includes the typical nitride-based materials such as silicon oxynitride or silicon nitride. In this preferred embodiment of the present invention, the hard mask nitride layer 37 has a thickness ranging from about 1000 Å to about 5000 Å.
Meanwhile, it is also possible to perform an additional process for forming a buffer layer (not shown) for reducing stress easily generated between the bit line metal layer 36 and the hard mask nitride layer 37. At this time, the buffer layer is made of undoped silicate glass (USG).
As shown in
A third inter-layer insulation layer 38 is deposited on the above structure including the bit line. The third inter-layer insulation layer 38 is called a bit line insulation layer. At this time, the third inter-layer insulation layer 38 is formed with any material selected from a group consisting of a boron-phosphorus silicate glass (BPSG) layer, a high temperature oxide (HTO) layer, a medium temperature oxide (MTO) layer, a high density plasma (HDP) oxide layer, a tetra-ethyl-ortho silicate (TEOS) layer or an advanced planarization layer (APL).
Next, a chemical mechanical polishing (CMP) process is performed with a target that the third inter-layer insulation layer 38 has the same height of the hard mask nitride layer 37 so as to make the third inter-layer insulation layer 38 planarized. Then, a wet etching process is performed by using a wet solution such as buffered oxide etchant (BOE) or HF. After the wet etching process, the height of the third inter-layer insulation layer 38 is lower than that of the hard mask nitride layer 37. This etched thickness is remarked as ‘X’ in
It is also noted that a dry etching process can be performed instead of the wet etching process. Furthermore, the third inter-layer insulation layer 38 is etched to a depth in a range from about 300 Å to about 1500 Å from an upper part of the hard mask nitride layer 37.
With reference to
A photoresist pattern 40 for a storage node contact (hereinafter referred to as a storage node contact photoresist pattern) is formed on the etch stop layer 39. At this time, the photoresist pattern is formed by employing a photo-exposure process using a light source of KrF or ArF. Also, the etch stop layer 39 is formed with a nitride-based material such as silicon nitride or silicon oxynitride. Also, the thickness of the etch stop layer 39 is preferably in a range from about 50 Å to about 1000 Å.
In addition, during the SAC process, such gas as C3F8, C4F8, C5F8, C3F3, C4F6 or C2F4 is used as a main etch gas to provide high etch selectivity during the SAC process. Also, such gas as CHF3, C2HF5, CH2F2 or CH3F can be also used as the etch gas for increasing a bottom side area of the storage node contact hole in order to improve reliability of the etch process along with the high etch selectivity. Additionally, oxygen gas or Ar gas can be also used as the etch gas for improving a stopping function of the etch process by increasing plasma stability and sputtering efficiency.
In contrary to the prior art wherein the SAC process is employed to form a spacer at a sidewall of the contact hole by etching the nitride-based etch stop layer, there is no spacer formed in accordance with the present invention.
Therefore, it is important to properly control the thickness and apply etch recipe based on a concerned design rule in order to secure an intended etch profile and simultaneously to block the etch stop layer 39 from remaining at the sidewalls of the contact hole 41.
Meanwhile, prior to forming the contact hole, a process for forming a contact pad can be additionally performed to improve an overlap margin of a contact formation process. However, detailed descriptions on this additional process are omitted.
A conductive material for a storage node contact (SNC) plug 42 (hereinafter referred to as a SNC plug conductive material) is deposited into the contact hole 41. The remaining etch stop layer 39 and the SNC plug conductive material are removed through a CMP process under an etch target of exposing a surface of the third inter-layer insulation layer 38 so to form the planarized and isolated SNC plug 42. As shown in
In the mean time, the oxide-based bit line insulation layer 38, i.e., the third inter-layer insulation layer, exists in between the SNC plug 42 and the bit line. Particularly, the oxide-based third inter-layer insulation layer has a lower dielectric constant than the nitride-based material used in the prior art. Therefore, a loading capacitance of the parasitic capacitor, constructed by the SNC plug 42, the bit line and the third inter-layer insulation layer 38, is decreased. This decreased loading capacitance provides a further effect of augmenting an overall cell capacitance.
In addition to the above-described preferred embodiment for forming the storage node contact plug with use of the SAC process, the present invention can be still applicable to various types of semiconductor device fabrication processes for which the SAC process is employed. A process for opening an active region between the gate electrodes is one example of applying the present invention to other processes.
While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.
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|U.S. Classification||438/706, 257/E21.507, 438/672, 257/E21.649, 257/E21.657, 438/720, 438/634|
|International Classification||H01L21/60, H01L21/302, H01L21/8242, H01L21/311|
|Cooperative Classification||H01L27/10855, H01L27/10885, H01L21/76897|
|European Classification||H01L27/108M4B2C, H01L21/768S|
|Jul 11, 2003||AS||Assignment|
Owner name: HYNIX SEMICONDUCTOR INC., KOREA, REPUBLIC OF
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